class Direction():

    NORTH = "NORTH"
    SOUTH = "SOUTH"
    EAST = "EAST"
    WEST = "WEST"
    STOP = "STOP"
    LEFT =       {NORTH: WEST,
                   SOUTH: EAST,
                   EAST:  NORTH,
                   WEST:  SOUTH,
                   STOP:  STOP}

    RIGHT =      dict([(y,x) for x, y in LEFT.items()])

    REVERSE = {NORTH: SOUTH,
               SOUTH: NORTH,
               EAST: WEST,
               WEST: EAST,
               STOP: STOP}